Alzheimer's Disease is a progressive and degenerative dementia (Terry, et al. (1991) Ann. Neurol. 30:572-580; Coyle (1987) In: Encyclopedia of Neuroscience, Adelman (ed.), Birkhäuser, Boston-Basel-Stuttgart, pp 29-31,). In its early stages, Alzheimer's Disease manifests primarily as a profound inability to form new memories (Selkoe (2002) Science 298:789-791), reportedly due to neurotoxins derived from amyloid beta (Aβ). Aβ is an amphipathic peptide whose abundance is increased by mutations and risk factors linked to Alzheimer's Disease. Fibrils formed from Aβ constitute the core of amyloid plaques, which are hallmarks of an Alzheimer's Disease brain. Analogous fibrils generated in vitro are lethal to cultured brain neurons. These findings indicate that memory loss is a consequence of neuron death caused by fibrillar Aβ.
Despite strong experimental support for fibrillar Aβ and memory loss, a poor correlation exists between dementia and amyloid plaque burden (Katzman (1988) Ann. Neurol. 23:138-144). Moreover, transgenic hAPP mice (Dodart, et al. (2002) Nat. Neurosci. 5:452-457; Kotilinek, et al. (2002) J. Neurosci. 22:6331-6335), which develop age-dependent amyloid plaques and, most importantly, age-dependent memory dysfunction, show that within 24 hours of vaccination with monoclonal antibodies against Aβ memory loss can be reversed with no change in plaque levels. Such findings are not consistent with a mechanism for memory loss dependent on neuron death caused by amyloid fibrils.
Additional neurologically active molecules formed by Aβ self-assembly have been suggested. These molecules include soluble Aβ oligomers, also referred to as Aβ-derived diffusible ligands or ADDLs. Oligomers are metastable and form at low concentrations of Aβ1-42 (Lambert, et al. (1998) Proc. Natl. Acad. Sci. USA 95:6448-6453). Aβ oligomers rapidly inhibit long-term potentiation (LTP), a classic experimental paradigm for memory and synaptic plasticity. As such, memory loss stems from synapse failure, prior to neuron death and synapse failure by Aβ oligomers, not fibrils (Hardy & Selkoe (2002) Science 297:353-356). Soluble oligomers have been found in brain tissue and are strikingly elevated in Alzheimer's Disease (Kayed, et al. (2003) Science 300:486-489; Gong, et al. (2003) Proc. Natl. Acad. Sci. USA 100:10417-10422) and in hAPP transgenic mice Alzheimer's Disease models (Kotilinek, et al. (2002) J. Neurosci. 22:6331-6335; Chang, et al. (2003) J. Mol. Neurosci. 20:305-313).
A variety of Alzheimer's Disease treatment options have been suggested. Vaccine clinical trials have revealed that persons mounting a vigorous immune response to the vaccine exhibit cognitive benefit (Hock, et al. (2003) Neuron 38:547-554); however, frequency of CNS inflammation caused early termination of part of the trial (Birmingham & Frantz (2002) Nat. Med. 8: 199-200). As an alternative to a vaccine, therapeutic antibodies that target ADDLs without binding monomers or fibrils have been suggested (Klein (2002) Neurochem. Int. 41:345-352). ADDLs are highly antigenic, generating oligomer-selective polyclonal antibodies in rabbits at concentration of ˜50 μg/mL (Lambert, et al. (2001) J. Neurochem. 79:595-605). Results from transgenic mice models also suggest that antibodies can be successful in reversing memory decline (Dodart, et al. (2002) Nat. Neurosci. 5:452-457). Accordingly, there is a need in the art for ADDL-selective therapeutic antibodies for the prevention and treatment of Alzheimer's Disease. The present invention meets this need.